Toronto, July 24 : Do you know why you instantly recall the smell of apple pie prepared way back by your grandmother as you walk into her kitchen? There is a scientific reason behind it.
Researchers have now discovered the mechanism behind how smells that one has experienced in the past have contributed in the formation of memories -- suggesting a novel perspective on the way senses are represented in memory.
The findings may explain why the loss of the ability to smell has been recognised as an early symptom of Alzheimer's disease and can offer opportunities for improved smell tests in Alzheimer's disease diagnosis.
"Our findings demonstrate for the first time how smells we've encountered in our lives are recreated in memory," said lead author Afif Aqrabawi from the University of Toronto.
"In other words, we have discovered how you are able to remember the smell of your grandma's apple pie when walking into her kitchen," Aqrabawi added.
For the study, published in the journal Nature Communications, the team examined the strong connection between memory and olfaction -- the process of smelling and recognising odours in the mice.
They found that information about space and time integrate within a region of the brain important for the sense of smell known as the anterior olfactory nucleus (AON).
While examining the function of AON, the team uncovered a previously unknown neural pathway between it and the hippocampus -- a structure critical for memory and contextual representation, and highly implicated in Alzheimer's disease.
Mice whose hippocampus-AON connection was left intact, refrained from returning to familiar locations to sniff odours that were no longer novel whereas those with a disconnected pathway returned to sniff previously smelled odours for longer periods of time.
"They prefer to spend more time smelling a new odour than one that's familiar to them.
When they lose this preference, it's implied they no longer remember the smell even though they have sniffed it before, so they continue to smell something as if for the first time," said Aqrabawi.
"...we now understand which circuits in the brain govern the episodic memory for smell.
The circuit can now be used as a model to study fundamental aspects of human episodic memory and the odour memory deficits seen in neurodegenerative conditions," he added.